Agriculture Reference
In-Depth Information
ed that about 20% of cultivated lands and 33% of irrigated agricultural
lands worldwide are afflicted by high salinity (Foolad, 2004; Ghassemi
et al., 1995; Szabolcs, 1992). Moreover, the salinized areas are increas-
ing at a rate of 10% annually; low precipitation, high surface evapora-
tion, weathering of native rocks, irrigation with saline water, and poor
cultural practices are the major contributors to the increasing soil salinity.
In spite of the physiological cause ion toxicity, water deficit, and/or nutri-
tional imbalance, high salinity in the root area sternly inhibits normal plant
growth and development, resulting in reduced crop productivity or total
crop failure (Ghassemi et al., 1995). Young seedlings and plants at an-
thesis appear to be more sensitive to salinity stress than the mature stages
(Lutts et al., 1995). Onions are sensitive to saline soils, while cucumbers,
eggplants, peppers, beet palak and tomatoes are moderately sensitive. To-
matoes grown under high salinity will produce smaller fruit with higher
soluble solids (Mizrahi, 1982). Smaller fruit will have higher surface area
to volume ratios, hence greater susceptibility to postharvest water loss
(i.e., desiccation stress) (Shibairo et al., 1997). While there is no direct
information in the literature to confirm that smaller tomato fruit from saline
growing conditions would be subject to greater desiccation stress posthar-
vest, firmness declines for tomatoes grown under 3 and 6 dS m -1 salinity
levels were increased by 50 to 130%, respectively, at two weeks holding at
20 °C compared with control fruit (Mizrahi et al., 1988).
8.3.6.6 FLOODING
Vegetables production starts at commercial level in many areas on onset
of monsoon, but production occurs in both dry and wet seasons. However,
production is often limited during the rainy season due to excessive mois-
ture brought about by heavy rain. Most vegetables are highly sensitive
to flooding and genetic variation with respect to this character is limited,
particularly in tomato, early cauliflower and karif onion. In general, dam-
age to vegetables by flooding is due to the reduction of oxygen in the root
zone, which inhibits aerobic processes. Flooded tomato plants accumu-
late endogenous ethylene that causes damage to the plants (Drew, 1979).
The rapid development of epinastic growth of leaves is a characteristic
response of tomatoes to water-logged conditions and the role of ethylene
accumulation has been implicated (Kawase, 1981). The severity of flood-
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